This invention relates to an automatic meter reader and more particularly to a meter reader which includes a microcomputer operating to accurately control accumulation of meter data, to implement and control telephone communication with a central station to report meter data and to perform auxiliary functions with a high degree of efficiency and reliability. The reader is very efficient, providing a long operating life from a low voltage battery supply and it uses relatively inexpensive components and is otherwise economically manufacturable. 2. Background of the Prior Art
A review of pertinent prior art is contained in an introductory portion of the specification of the Thornborough et al. U.S. Pat. No. 4,817,131 issued Mar. 28, 1989 and in the introductory portion of the specification of the Thornborough et al. U.S. Pat. No. 4,866,761 issued Sept. 12, 1989, the disclosures of which are incorporated by reference. Said Thornborough et al. patents disclose automatic meter reader systems which have a number of highly advantageous features and in which "AMR" units are arranged for connection to customer's telephone lines and for automatic dialing for transmission of meter data to a computer of a utility control center. Each AMR unit is battery-operated and includes a microcomputer which is powered up periodically for a short time interval to store data, determine whether a call to the utility control center should be instituted and to determine whether leakage, tamper or other conditions require an immediate call.
Each AMR unit includes telephone interface and power supply circuitry connected to "tip" and "ring" telephone line terminals and to battery terminals. A modem circuit is provided which is operative as either a modulator or a demodulator and which has an input connected to the tip terminal. When operative as a modulator, the modem circuit responds to digital signals applied on a "TXD" line to send frequency shift modulated signals out on the telephone line. When operative as a demodulator, it detects the existence of a carrier signal on the telephone line to develop a signal on a carrier detect line and, in response to a frequency shift modulated signal on the telephone line, it develops a corresponding digital signal on a "RXD" line. A disabling "squelch" signal is applied to the modem circuit at certain times, through a "SQT" line.
Each AMR unit also includes a dial tone detect circuit which responds to a dial tone signal on the tip terminal to develop a signal on a dial tone line. The dial tone detect circuit as well as the modem circuit require a relatively high current for operation and are energized only in an off-hook condition so that they do not normally draw battery current.
The AMR units as disclosed in said patents include additional circuits which are energized at all times and which register meter pulse and monitor conditions, such circuits having very low current consumption. Such additional circuits include a clock circuit; a wake-up timer circuit which responds to clock pulses applied thereto; a meter pulse counter which responds to meter pulses applied from a meter terminal; a status register circuit which has an input connected to monitor the telephone interface circuit and inputs connected to switches for detection of tamper and freeze conditions; and a reset and power control circuit.
A random access memory portion of the microcomputer is also energized at all times, in both a "sleep" condition and a power-up or active condition. However, other circuits, including the main processing circuitry of the microcomputer and serial input-output circuitry associated therewith, are operative only in the power-up condition which is established periodically for short intervals to store accumulated data, or to make a scheduled report or in response to incoming calls or tamper conditions.
Ordinarily, in the absence of a tamper alarm and except when a scheduled report is due, the microcomputer is operated to the power-up condition periodically, e.g., every 5 minutes, in response to a signal applied from the wake-up timer. The microcomputer then increments a 5 minute interval register, adds the meter count from the preceding 5 minute interval to a total count register, adds counts to or updates time-of-day and peak rate registers, as appropriate, and then returns to the sleep condition.
When a scheduled report is due, the microcomputer initiates an operation in which a signal is applied to establish an off-hook condition and to then wait for a signal from the dial tone detector. Then a pulse-dialing operation is performed to dial a number assigned to the utility control center and the microcomputer then waits for a signal on the carrier detect line from the modem circuit. Then the microcomputer applies a squelch signal to the modem circuit it then proceeds to apply signals through the "TXD" line to the modem circuit to cause the modem circuit to send FSK modulated signals to the utility control center and thereby send data thereto. Then the microcomputer monitors the "RXD" line from the modem circuit, for receipt of an acknowledgement character and data from the utility control center. After data is sent back and forth in this way to effect a complete scheduled report transaction, the microcomputer operates to set the wake-up timer, makes a final phone/tamper check and then returns to the sleep condition.
The systems of said Thornborough et al. patents include a number of other advantageous features as set forth in detail therein.